In addition to one-to-one communication, or unicast, services such as phone calling and web browsing, modern mobile cell networks can be used for one-to-many services. Generally speaking, there are two types of one-to-many services: broadcast services, which are available to anyone, and multicast services, which are available only to those users who have subscribed for such services.
Broadcast and multicast services require several different techniques from traditional unicast services. In the unicast approach, multiple streams of the same content are delivered individually from the content provider. However, in the broadcast and multicast approaches, a single stream of content is delivered to multiple users. In broadcast and multicast services, the network has to distribute the data using IP multicast, while the encryption techniques have to ensure that all subscribing users can receive the information stream. To implement these techniques, the Universal Mobile Telecommunications System (UMTS) has developed the use of multimedia broadcast/multicast service (MBMS). MBMS is a one-to-many interface specification for existing and upcoming 3rd Generation Partnership Project (3GPP) cellular networks which is designed to provide efficient delivery of broadcast and multicast services, both within a cell as well as within the core network.
The long-term evolution (LTE) MBMS was introduced in 3GPP Release 9 and is known as evolved MBMS (eMBMS). The advantage of eMBMS over other traditional broadcast technologies such as Digital Video Broadcasting-Handheld (DVB-H), Digital Multimedia Broadcasting (DMB), and other broadcast services is that a minimal amount of additional network infrastructure is required because eMBMS can be implemented into the existing cellular networks. So, the cost of eMBMS implementation would be minimal as it would be able to use the existing LTE infrastructure.
To transmit eMBMS data streams, LTE uses an air interface technique known as multicast/broadcast over a single frequency network (MBSFN). This technique employs nearby base stations which are synchronized so that they broadcast the same content at the same time and on the same sub-carriers. As a result, the signals from the different base stations arrive within the cyclic prefix of the user element, and the resulting signal will appear to the user element as one transmission, which contributes to the received signal power.
In LTE, these synchronized base stations lie in a region known as an MBSFN area. MBSFN areas can overlap, so that one base station can transmit multiple sets of content from multiple MBSFN areas. In one MBSFN area, the same content is transmitted to multiple users. One cell in a cellular network may belong to more than one MBSFN area (up to 8).
In each MBSFN area, the LTE air interface delivers the eMBMS using a multicast traffic control channel (MTCH) and a multicast control channel (MCCH). Each MBSFN area contains one MCCH and multiple instances of the MTCH. The MTCH carries the broadcast traffic such as the multimedia data, while the MCCH is the control channel which carries the radio resource control (RRC) signaling messages needed for receiving the MTCH. The MCCH carries the MBSFN Area Configuration message, which is the basis for scheduling MBMS services and providing information on Common Subframe Allocation (CSA) and the multicast channel (MCH) scheduling period. In other words, the MTCH provides the data, while the MCCH provides the instructions for receiving the data. Both the MCCH and the MTCH use the MCH as a transport channel and the physical multicast channel (PMCH) as the physical channel.
However, a problem is encountered when an ongoing eMBMS reception is interrupted by an incoming transmission (e.g. phone call) in, for example, a multi subscriber identity module (SIM) device that uses a cost optimized Hybrid dual-reception, dual-SIM dual-standby (DR-DSDS) platform or the like. If the eMBMS reception is occurring in the reception/transmission main (RX/TX MAIN) radio frequency (RF) path, then the eMBMS reception must be switched to the reception auxiliary (RX AUX) RF path in order to allow for the incoming transmission to take place on the RX/TX MAIN RF path. However, switching the eMBMS reception from the RX/TX MAIN path to the RX AUX path can contribute to an interruption in eMBMS reception that can last up to about 2.5 seconds, which may be of great inconvenience to the end user.
Thus, there remains a considerable need to mitigate the interruption caused by an incoming transmission while there is an ongoing reception in a communication device.